browne



United States Patent 2,7 33,316 ARC-EXTINGUISHING DEVICES Thomas E. Browne, Jr., and Albert P. Strom, Forest Hills,

Application September 14, 1954, Serial No. 455,976 21 Claims. (Cl. 200-148) This invention relates to arc-extinguishing devices in general, and, more particularly, to improved arc-extinguishing structures.

A general object of our invention is to provide a circuit interrupter, or a fuse structure, embodying selenium hexafiuoride gas, whereby vastly improved interrupting performance is obtained.

Another object is to provide an improved circuit interrupting apparatus or fuse structure embodying selenium hexafluoride gas as the arc-interrupting medium, in conjunction with means for blowing the selenium hexafiuoride gas through electrical arcs therein.

The use of sulfur hexafluoride (SP6) gas as an arcextinguishing medium has been described and claimed in United States patent application, Serial No. 237,502, filed July 19, 1951, entitled Circuit lnterrupters by Harry J. Lingal, Thomas E. Browne, Jr., and Albert P. Strom, and assigned to the assignee of the instant application. In this patent application suggesting the use of sulfur hexafluoride as an arc-extinguishing medium, phenomenal results are achieved. For example, in a 3-inch-long arc in sulfur hexafluoride, the interrupting ability of SP6 is 100 times that in air, and, utilizing a puffer to obtain a blast of SFs, an interrupting ability of 20,000 times that obtained by still air is obtained. Commercial apparatus, embodying SP6 is being manufactured utilizing its unusual properties, such an apparatus being that set out in U. S. patent application, filed October 26, 1951, Serial No. 253,321, by Harry J. Lingal, and assigned to the assignee of the instant application.

The present application is concerned with a new interrupting gas having in some respects similar properties to those of SFs, and it is proposed to use this new gas SeFs as the interrupting and insulating medium in either a circuit interrupter or a fuse structure.

Further objects and advantages will readily become apparent upon reading the following specification, taken in conjunction with the drawings, in which:

Figure 1 is a vertical sectional view through an explosion pot type of circuit interrupter utilizing SeFe as the arc-extinguishing medium, the contact structure being shown in the partly open-circuit position;

Fig. 2 is a vertical sectional view through a modified type of circuit interrupter utilizing a puffer piston for driving SeFs through the established arc, the contacts being shown in the closed-circuit position;

Fig. 3 is a vertical sectional view through a plain-break circuit interrupter, which was utilized in experimentally obtaining data hereinafter described, the contact structure being shown in the closed-circuit position;

Fig. 4 illustrates graphically the experimental results obtained utilizing the experimental setup of Fig. 3, and comparing the performance of selenium hexafiuoride at different voltages and pressures with that of air;

' Fig. 5 is a vertical sectional view through an enclosed circuit interrupter of the splitter type, in which the established arc is moved laterally against a plurality of spaced insulating splitters, illustrated in the closed-circuit Fig. 6 is a side elevational view, partially in vertical section, of a gas-blast type of circuit interrupter employing stored selenium hexafiuoride under pressure; and

Fig. 7 is a somewhat diagrammatic view of a fuse structure incorporating a fusible element enclosed in a suitable container, within which is disposed selenium hexafiuoride under a suitable pressure for effecting arc interruption upon fusing of the fusible element.

Referring to the drawings, and more particularly to Fig. 1 thereof, there is illustrated an interrupter device wherein the reference numeral 1 designates a porcelain casing, within which is disposed a stationary contact 2, and a movable rod-shaped contact 3 passes through a closure 4 applied to the upper end of the casing and is guided by a bushing 4A. The contact is actuated externally of the casing 1 by any suitable mechanism (not shown).

it will be noted that the stationary contact 2 is dis posed interiorly within an explosion chamber comprising an insulating cylinder 5 threaded, as at 6, to a metallic cup 7 disposed at the lower end of the casing 1. A cap 8 encloses the lower end of easing 1, and is apertured at to permit a tubular extension 1b of the stationary contact 2 to pass therethrough. A line terminal 11 may be connected to this extension 10, whereas the other line teminal for the interrupter may be connected, as by a slide connection, or otherwise, to the movable contact 3. The casing 1, closure 3 and cap 8 provide a hermetically sealed interrupting device.

A conduit 12, sealed ofi after filling, or provided with suitable valve means (no-t shown), is attached to the closure 4 to permit the filling of the casing 1 with selenium hexailuoride gas from a source of supply thereof, or a gas mixture containing selenium hexafiuoride gas. While an initial filling of the selenium hexafiuoride gas should be sufficient for the normal life of the interrupter, leakage or other loss may require subsequent replenishment. Perforated copper cooling plates 13 are provided for cooling the gases when subjected to arcing. The cooling plates are rigidly aifixed, as by soldering, to a metallic cylinder 14 disposed interiorly within the lower end of the explosion chamber 5.

An insulating orifice member 15, threaded, as at 16, to the upper end plate 17 of the explosion chamber 5, is provided to permit passage of contact 3 therethrough and to direct a stream of the selenium hexafluoride gas against the arc, which, for purposes of illustration, is represented by the reference character 18.

In the operation of the device, the movable contact 3 is caused to separate from the stationary contact 2, and since it substantially closes the opening 19 through the orifice member 15, pressure is generated in the body of selenium hexafluoride gas within the explosion chamber 5 by the heat of the established arc. Following withdrawal of the movable contact 3 out of the opening 19 of the orifice member 15, there occurs a stream or blast of the compressed selenium hexafluoride gas escaping from the explosion chamber 5. The stream of selenium hexafiuoride gas is directed through the arc and quickly effects extinction of the are 18, and hence circuit interruption is obtained.

Since some free fluorine may be temporarily liberated from the selenium hexafluoride gas during the interrupting operations, it is not desirable to use insulating orifices or other parts adjacent the arc of organic materials, such as horn fiber. Hydrogen, evolved from the fiber during arcing, will react with the free fluorine to produce highly reactive hydrogen fluoride acids. We have discovered a solution to the difiiculty of preventing the formation of corrosive hydrogen fluoride acids by employing insulathe contact structure being position;

tion composed of either polytetrafluoroethylene or polymonochlorotrifiuoroethylene. These fiuorinated polymer materials have been found suitable for orifice materials, and are barriers such as the cylindrical piece A of Fig. l to protect the main body of the organic insulating material forming the cylinder 5 from the heat of the arc. Also barrier discs 53 and 5C of these fiuorinated polymers may be employed to protect the organic insulating material from the heat of the arc.

, Accordingly, the insulation to be exposed to the arcs in circuit interrupters embodying selenium hexafluoride is preferably composed entirely of, or surfaced with, a solid polymer selected from the group consisting of polytetrailuoroethylene and polychlorotrifluoroethylene. The polymers have the unit formula I C Q I I F X where X represents a halogen selected from the group consisting of chlorine and fluorine.

Fig. 2 indicates a modified type of interrupter using selenium hexafiuoride gas and employing a piston movable with the movable contact for causing forced gas flow against or through the drawn arc. This is known as a puffer type of interrupter. The reference character 21 indicates a porcelain cylinder having a perforated top end cap 22 having a bushing 23, through which a movable contact rod 24 moves, under the influence of a mechanism (not shown), externally of the bushing 21.

Secured to the movable contact rod 24 is a piston, generally designated by the reference character 25, and including an insulating cylinder 26. An orifice member 27 of polytetrafiuoroethylene, for instance, is disposed at one end of piston 25, being retained in place between a washer-shaped member .23 and an insulating cap 29. An internal shoulder 30 is provided at the lower end of the insulating cylinder 26 against which an outwardly turned flange 31 of a tubular member 32 is placed. The cap 29 is threadedly connected to the lower end of the insulating tube 32.

Spacing the upper side of the washer member 28 from the top of the piston is a spacing sleeve 33, having the upper end thereof bearing against an apertured plate 34 having apertures 4-3 therein. The bottom side of the washer member 28 abuts the insulating tube 32 and holds it against the shoulder 30.

The insulating cylinder 26 is threadedly connected, at 35, to an insulating cylindrical extension 36, which extension is secured, as by threading or by a press fit, as shown, to the apertured plate The piston 25 slides Within a space 47 in a cooperating cylinder 37, the upper end of which is secured by one or more screws to a washer 3h, threadedly engaged at to a metallic bushing 41. The operating cylinder 37 has a channel 42 provided therein to register with a conduit 12, the latter being provided to allow introduction of selenium hexailuoride gas to the interior of the casing 21. The lower end of the movable contact rod 24 carries a movable contact 43, which makes abutting engagement,

as shown, with a stationary contact member 44., the. latter being secured to an apertured lower end plate 45 closing the lower end of the casing 21. A line terminal 11 is secured to an extension 46 of the stationary contact member 44.

The operation of the breaker of Fig. 2 is as follows: During the circuit opening operation, the movable contact rod 24 is moved upwardly by a suitable external actuating mechanism not shown. The upward movement of the movable contact rod 24 not only effects separation between the contacts 43, 44 drawing an arc therebetween, but also moves th piston 25 within the interior of the operating cylinder 3.7, thereby causing the selenium hexafluoride gas within the space 47 to pass through the apertures 48, provided in the plate 34, and interiorly through the piston 25 and thence through the orifice member 27 where the flow of selenium hexafluoride gas is constricted into engagement with the arc. The flowing stream of selenium hexailuoride gas enables a prompt and efiicient extinction of the arc.

Tests were made in the porcelain tube, plain-break interrupter of Fig. 3 of the drawings. This interrupter had 0.5 inch diameter rod contacts tipped with coppertungsten. The stationary contact is indicated by the reference numeral 50, whereas the movable contact is designated by the reference numeral 51., having its shank portion 52 movable through a sealing gland 53 by means of a pneumatically operated piston 54 moving within a pneumatically operating cylinder 55. The selenium hexafluoride gas supplywas connected to a conduit 56 controlled by a valve 7, whereas another connection 58, con ed by a valve 59, led to a manometer and gas measuring equipment, or permitted flushing of the chamber enclosed by the porcelain cylinder 60. Line connections are indicated at 61 and 62, the first of which being secured to and movable with the movable rod contact 51, whereas the other line connection 62 was bolted to the lower closure cap 63 of the device. A contact separation of three inches was employed, with an average opening speed of to inches per second. The interrupting tests were made with a reactive circuit at 1150, 2300, 4600, 6900 and 13,800 nominal volts. Pressures from atmospheric through 45 p. s. i. gauge were used.

Tests were called successful if interruption of the circuit occurred in less than a prescribed number of half cycles of arcing-in this case 7, 4 or 5 half cycles after full contact separation. The currents Were symmetrical. The interrupting current limit was taken to be just above the highest test value at which at least four successful interruptions, or at least seven interruptions with no more than one failure, were obtained.

Fig. 4 graphically illustrates some of the test results obtained using the selenium hexafluoride at different pressures and voltages, compared with air at 1150 volts for various pressures, as indicated by the dotted line 66 of Fig. 4.

It will be observed that the results obtained using selenium hexafiuoride are phenomenal, as compared with the plain-break apparatus utilizing air as the interrupting medium.

In a series of tests with the gas at pressures between zero and 45 p. s. i. gauge, it was found the 60-cycle alternating currents in a lower power factor reactive circuit could be interrupted with current magnitudes in the order of 100 times the limiting values for interruption when the interrupter was filled with air. For example, with air at 30 p. s. i. gauge pressure, the current interrupting ability in a 2300-volt reactive circuit was about 1.5 amperes R. M. S. When filled with SeFs gas at 30 p. s. i. g. pressure, a current of amperes R. M. S. was interrupted five times without a failure by the same interrupter in the 2300-volt reactive circuit. Failures were obtained only when the current was increased to 198 amperes.

The dielectric strength of selenium hexafluoride is slightly higher than that of sulfur hexafluoride (2.9 times he st engt o ai ompa h ime f SP The chemical stability of selenium hexafluoride, when heated in the presence of metals and Pyrex glass, is comparable with that of SFs. Its boiling point is reported as -34.5 C. With a molecular weight of 193, it is about 6.6 times as dense as air in the vapor state.

Fig. 5 shows a magnetic type circuit interrupter using selenium hexafluoride gas, and employing insulating arc splitter plates. Referring to Fig. 5, it will be observed that there is provided a cup-shaped insulating enclosure 8 1 attached by bolts 82 to a baseplate 33, gas-tight gaskets 8% being disposed between the base plate and enclosure 8 1, the assembly thereby being hermetically sealed.

Within the enclosure is a U-shaped magnetic member 85, with a blowout coil 86 encircling a yoke portion 87 of the magnetic member 85. Only one pole plate 88 of magnetic members 85 is shown. Between the pole plates 88 are a pair of arc horns 89, 98, the arc horn 98 being electrically connected to one end of the coil 86. The other end of the coil 86 is connected by a strap connection 91 to a stationary contact 92 of the interrupter. The stationary contact 92 has a shank portion 93 extending through the base plate 83, to which an external line connection 94 is fastened.

Cooperable with the stationary contact 92 is a movable contact 95, which is mounted on an operating shaft 96 hingedly connected to a bifurcated bracket 97, the latter also extending through the base plate 83 and having a line terminal 98 connected thereto. The shaft 96 may be rotated externally of the casing 81 by any suitable means, either manually or automatically to rotate the movable contact 95 to open and closed-circuit positions. A flexible strap 99 connects the movable contact 95 to the arc horn 89.

Preferably, we employ in this embodiment of our invention insulating arc splitters 100, composed of the fluorinated polymers previously disclosed, spaced apart and having their side edges secured to a pair of lengthwise extending insulating side plates 101, by cement or otherwise.

During the opening operation, a crank is employed to rotate the shaft 96 counterclockwise, which eflFects separation between the stationary and movable contacts 92, 95 to draw an arc therebetween. The arc, which is drawn therebetween, strikes the arc horn 90, and, because of the shunt path through the coil 86, the arc portion extending between the stationary contact 92 and the arc born 90 is extinguished. The terminal of the remaining arc, attached to the movable contact 95, soon attaches to the left-hand arc horn 89, so that the resulting are, indicated by the reference character 102, moves upwardly under the influence of the transverse magnetic field into engagement with the lower ends of the arc splitters 100. The combination of selenium hexafiuoride gas and the arc splitters readily interrupts the are 102. The combination will produce unusually efiective arc interruption.

Fig. 6 represents an embodiment of our invention comprising a gas blast breaker utilizing selenium hexafiuoride stored under pressure. A reservoir tank 191 containing selenium hexafiuoride gas under pressure is utilized, with a blast valve 192 operated by an actuating link 193.

The arc, which is established between a movable contact 210 and a stationary contact 211, is drawn axially through a bore 212 of an insulating orifice member 213. The contact 210 is slightly spaced from the walls of the orifice member 213 to permit selenium hexafiuoride gas to pass by. The orifice member 213 may be secured by a press fit within an insulating blast tube section 214, the lower end of which is threadedly secured, as at 215, to a conducting perforated spider 216. The conducting spider 216 has upper and lower flange portions 217, 218 which are respectively secured to the blast tube section 214 and to a lower blast tube section 219.

It will be observed that the movable contact 210 is affixed to a piston 220 which moves axially within a conducting operating cylinder 221, at the upper end of which is secured a line terminal 222. The operating cylinder 221 has an opening 223 which is uncovered upon sufficient upward movement of the piston 220. A compression spring 224 is provided to bias the piston 220 downwardly, and hence the contact structure, to the closed-circuit position.

Associated with the conducting spider 216 is a stationary disconnect contact 225 cooperable with a movable disconnect blade 226, the latter being rotatably mounted, as at 227, on a terminal plate 228, to which a line connection may be made.

The exhaust opening 223 leads into a chimney 229 within which is disposed a cooler 230 consisting of copper wool, or other cooling material. The chimney 229 has an upper insulating section 231 associated therewith which may extend within an enclosure 234, from which the gas may be drawn through a pipe 235 to a compressor 236. The gas, after recompression is fed back to the reservoir tank 191.

The operation of the interrupting device is as follows. Upon opening the blast valve 192 by operation of the actuating link 193, selenium hexafiuoride gas under pressure passes upwardly through the blast tube section 219, past the spider 216, and through the orifice member 213 to act upwardly upon the movable piston 220. When the gas pressure below the piston 220 is sufficient to raise it, in opposition to the biasing action exerted by the compression spring 224, the contacts 210, 211 will become separated and will draw an arc axially through the bore 212 of the insulating orifice member 213.

The blast of selenium hexafiuoride gas passing upwardly through the orifice member 213 will rapidly extinguish the are drawn between the contact structure, and the gas will exhaust outwardly through the exhaust opening 223 which will have been uncovered at this time by upward displacement of the piston 220. Any are flame will be cooled by the copper wool within the cooler 230, and any corrosive gases will be absorbed in the absorber 233. The remaining gas will be recompressed by the compressor 236.

In order to maintain the electrical circuit open upon closure of the blast valve 192, the serially related disconnect switch 225, 226 is provided. Thus upon closure of the blast valve 192, the compression spring 224 will effect closure of the contact structure, and the disconnect switch blade 226 may be maintained in its open position to cause the electrical circuit to remain open even though the contact structure within the interrupter has been closed.

Thus, in this embodiment of our invention we show an application of the use of selenium hexafiuoride gas under pressure in an axial blast type of circuit interrupter, in which the selenium hexafiuoride gas may be repeatedly used.

Fig. 7 illustrates a fuse structure 240 utilizing selenium hexafiuoride as the arc-extinguishing gas for extinguishing the are established upon fusion of the fusible element 241. This element is electrically connected at its ends to the caps 242, 243 at the ends of the casing 244, which may be of any suitable insulating material, preferably polytetrafluoroethylene or polymonochlorotrifluoroethylene. Other insulating materials may, however, be employed, but we believe that preferable results are obtained utilizing the two materials mentioned.

As indicated in the drawings, various types of circuit interrupters and fusible structures may be employed utilizing selenium hexafiuoride either in the pure state or mixed with other gases. The admixed gases may include air, nitrogen, hydrogen, argon, helium and carbon dioxide. Sulfur hexafiuoride may also be mixed with the selenium hexafiuoride. Preferably, 50% of the gas is selenium hexafiuoride, although advantage may be taken of its interrupting ability with other proportions.

From the foregoing, we have disclosed how selenium hexafiuoride may be employed alone or admixed with other suitable gases for arc-extinguishing purposes. We have indicated in Fig. 4 the exceptional interrupting performance, as compared with air, and it appears to be an exceptional arc-extinguishing gas.

Although we have shown and described specific structures in combination with a particular gas, it is to be clearly understood that the same were merely for the purpose of illustration, and that changes and modifications may readily be made therein by those skilled in the art without departing from the spirit and scope of the inventio'nl We claim as our invention:

1. An arc extinguishing device including as an are extinguishing medium a gas comprising selenium hexa- Z fluoride, and: means for. establishing an arcv within. said medium, the medium being capableof eiiecting extinction of thearc.

2. An arc extinguishing devices including means for establishing an are, means for forcing a blast of gas against the arc to effect the extinction thereof, and the gas, comprising selenium hexafluoride.

3. An arc extinguishing device including an enclosure containing essentially selenium hexafluoride gas and means between which the arc is, established within the enclosure, the. selenium hexafluoride. gas being capable of efliecting extinction of the are.

4'. An arc extinguishing device including an enclosure containing selenium hexafluoride gas, means for establishing an arc within the enclosure, and means for forcing the selenium, hexafluoride gas. against the arc to efiect the extinction thereof.

5. An arc extinguishing device including an enclosure, means providing an orifice therein, means for establishing an arc adjacent'the orifice, and means for forcing gas thrQl gh the orifice into engagement with the established arc to effect the extinction thereof, said gas comprising selenium hexafiuoride;

6 An arc extinguishing device including an enclosure, means for establishing an arc within the enclosure, a plurality of spaced arc splitters, means for causing the arc to be moved against the plurality of arc splitters, the enclosure containing a gas comprising selenium hexafluoride, and the selenium hexafluoride gas cooperating with the arc splitters to extinguish the arc.

7; An arc extinguishing device including an enclosure containing a substantial proportion of selenium hexafluoride gas, means for establishing an are within the enclosure, a plurality of arc splitters, and magnetic blowout means for forcing the arc against the arc splitters to effect the extinction thereof by the cooperation of the selenium hexafiuoride gas and the arc splitters within the enclosure.

8. An arc extinguishing device including an enclosure containing gas comprising selenium hexafiuoride, means providing an explosion pot within said enclosure, a stationary contact disposed within the explosion pot, a movable contact; movable into engagement with the stationary contact and away therefrom to a position externally of the explosion pot, and the generation of gas pressure within the explosion pot effecting extinction of the arc drawn thereout.

9. A circuit interrupter including an enclosure containing a substantial proportion of selenium hexafluoride gas, a stationary contact disposed within the enclosure, a movable contact carrying a piston and cooperable with the stationary contact to establish an arc, an operating cylinder Within which the piston is movable, and the opening of the movable contact not only establishing an arc between the stationary and movable contacts, but

also effecting working motion oi the piston within the operating cylinder to effect a flow of the selenium hexafluoride gas adjacent the established arc whereby to extinguish the arc.

10. A circuit, interrupter including a reservoir of gas under pressure, said gas comprising selenium hexafluoride, means for establishing an arc, and means for releasing a portion of said gas under pressure to effect extinction o h re 11. A circuit interrupter of the gas blast type including a reservoir containing gas comprising selenium hexafiuoride under pressure, orifice means, means for estabiishing an are through said orifice means, and blast valve mean for releasing a portion of said selenium hexafluoride gas through the orifice means to effect extinction of he ar the ei 12. An arc extinguishing device including as an arc extinguishing medium a gas comprising selenium hexaiiuoride, meansbetween which an arc is formed interruption of the circuit, and are confining and extinguishing means disposed along. the path of the are for extinguishing the are. in cooperation with the selenium hexatiuoride, the, arc confining and extinguishing means comprising a polymer of fluorinated ethylene selected from the group consisting of polytetrafiuoroethylene and polychlorotrifluoroethylene.

13. A circuit interrupter including means for establishing an are within a gas comprising selenium hexafluoride, insulating means disposed adjacent the established arc to assist the selenium hexafluoride in eifecting the extinction thereof, said insulating means being formed of a polymer of fluorinated ethylene selected from the group consisting of polytetrafluoroethylene and polychlorotrifluoroethylene.

14, A circuit interrupter including an enclosure containing selenium hexafluoride gas, a chamber disposed within the enclosure having an orifice associated there.- with, means for establishing an are through the orifice, and means for producing a blast of selenium hexafluoride gas passing through the orifice to extinguish the arc.

15 A circuit interrupter. including means defining an orifice, means for establishing an are adjacent the orifice, and means for forcing a gas comprising selenium hexatluoride through the orifice and adjacent the arc to effect the extinction thereof; 7' i 16. A circuit interrupter including an enclosure containing selenium hexafluoride gas, a chamber disposed within the enclosure having an orifice associated therewith, means tor establishing an arcfthrough the orifice, means forv producing ablast of selenium hexafluoride gas passing through the orifice to extinguish the arc, and the orifice being formed at least'i n part 'of'polytetr'afluoroethylene. M i

17. A circuit interrupter including means defining an orifice, means for establishing an arc adjacenhthe -orifice, means for forcing a gascomprising selenium'hexafluoride through the orifice and adj acent the arcto effect the extinction thereof, d the orifice being formed at leastinpart of polytctrafluoroethylene.

l-EYA circuit interrupter including an enclosure containing a substantial proportion of selenium hexafluoride gas, a stationary contact disposed within the enclosure, a movable contact carrying a piston and cooperable with the stationary contact toestablish an arc, the piston having an orifice associated therewith, an operating cylinder Within which the piston is movable to force the, gas through said orifice adjacent the arc, and theopening of the movable contact not only establishing an are between the stationary and movable contacts, but also effecting working motion of the piston within the operating cylinder-i0 efiect a flow of the selenium hexafiuoride gas through the orifice adjacent the established arc whereby to extinguish the arc. l9QA circuit interrupter including an enclosure con: taining a substantial proportion of selenium hexafluofride gas, a stationary contact disposed within the enclosure, a movable contact carrying a piston and cooperable with the stationary contact to establish an arc, thepiston hav ing an orifice assoc ated therewith, an operating cylinder within which the piston is movable to force the gas through said orifice adjacent the arc,the opening of the mouable contact not only establishing an'arc' between the stationary and movable con act s, but also efiecting working motion of the piston within the operating cylin der to etfect a flow of the selenium hexafiuoride gas through the orifice adjacent the established arc whereby to extinguishthe arc,'tbe orifice being formed at least in part of polytetrafluoroethylene, whereby corrosive acids will not be termed by the decomposition products nles sm h r lwr d 2 0. A circuit interrupter including an enclosure conais ns a s b ant a Pr ort on o s eni m x fl s gas, a stationary contact disposed enclosure, a movable contact carrying a piston having an orifice and cooperable with the stationary contactto establish an arc, the stationary contact extending at least part way through the orifice in the closed-circuit position, an operating cylinder within which the piston is movable, and the opening of the movable contact not only establishing an are between the stationary and movable contacts, but also effecting Working motion of the piston within the operating cylinder to eifect a flow of the seleniurn hexafiuoride gas through the orifice adjacent the established arc whereby to extingush the arc.

21. A circuit interrupter including an enclosure containing a substantial proportion of selenium hexafluoride gas, a stationary contact disposed within the enclosure, a movable contact carrying a piston having an orifice and cooperable with the stationary contact to establish an arc, the stationary contact extending at least part Way through the orifice in the closed-circuit position, an operating cylinder within which the No references cited. 

1. AN ARC EXTINGUISHING DEVICE INCLUDING AS A ARC EXTINGUISHING MEDIUM A GAS COMPRISING SELENIUM HEXAFLUORIDE, AND MEANS FOR ESTABLISHING AN ARC WITHIN SAID MEDIUM, THE MEDIUM BEING CAPABLE OF EFFECTING EXTINCTION OF THE ARC. 